First, find how much he paid by tire.
To do so, divide what he paid by how many tires he bought like this :
240$ / 12 = 20$ per tire
Then, calculate how much he sells each tire.
To do so, start by calculating how much he paid for 3 tires:
20$ x 3 = 60$
This is the price he sells 2 tires for, therefore :
60$ / 2 = 30$
he sells his tires 30$ each.
Finally, you have to calculate the profit he made by selling 12.
We already know how much it cost, so you need to find how much money he gets selling them :
12 tires x 30$ = 360$
To find the profit, take off the amount he paid from the amount he made :
360$ - 240$ = 120$
There you go!
